The present invention relates to elevator drive machines and more specifically to an elevator drive machine having a rotating traction sheave between rotors of multiple motors along the axis of rotation.
The drive machine of a traction sheave elevator has a traction sheave with grooves for the hoisting ropes of the elevator and an electric motor driving the traction sheave either directly or via a transmission. Traditionally the electric motor used to drive an elevator has been a d.c. motor, but increasingly a.c. motors, such as squirrel-cage motors with electronic control are being used. One of the problems encountered in gearless elevator machines of conventional construction has been their large size and weight. Such motors take up considerable space and are difficult to transport to the site and to install. In elevator groups consisting of large elevators, it has sometimes even been necessary to install the hoisting machines of adjacent elevators on different floors to provide enough room for them above the elevator shafts placed side by side. In large elevator machines, transmitting the torque from the drive motor to the traction sheave can be a problem. For example, large gearless elevators with a conventional drive shaft between the electric motor and the traction sheave are particularly susceptible to develop significant torsional vibrations due to torsion of the shaft.
Recently, solutions have been presented in which the elevator motor is a synchronous motor, especially a synchronous motor with permanent magnets. For example, the specification of WO 95/00432 presents a synchronous motor with permanent magnets which has an axial air gap and in which the traction sheave is directly connected to a disc forming the rotor. Such a solution is advantageous in elevator drives with a relatively low torque requirement, e.g. a hoisting load of about 1000 kg, and in which the elevator speed is of the order of 1 m/s. Such a machine provides a special advantage in applications designed to minimize the space required for the elevator drive machine, e.g. in elevator solutions with no machine room.
The specification of FI 93340 presents a solution in which the traction sheave is divided into two parts placed on opposite sides of the rotor in the direction of its axis of rotation. Placed on both sides of the rotor are also stator parts shaped in the form of a ring-like sector, separated from the rotor by air gaps.
In the machine presented in the specification of FI 95687, the rotor and the stator parts on either side of it with an air gap in between are located inside the traction sheave. In this way, the traction sheave is integrated with the rotor, which is provided with magnetizing elements corresponding to each rotor part.
The specification of DE 2115490 A presents a solution designed to drive a cable or rope drum or the like. This solution uses separate linear motor units acting on the rim of the drum flanges.
For elevators designed for loads of several thousand kg and speeds of several meters per second, none of the solutions presented in the above-mentioned specifications is capable of developing a sufficient torque and speed of rotation. Further, problems might be encountered in the control of axial forces. In motors with multiple air gaps, further difficulties result from the divergent electrical and functional properties of the air gaps.
This imposes special requirements on the electric drive of the motor to allow full-scale utilization of the motor. Special requirements generally result in a complicated system or a high price, or both.
The specification of GB 2116512 A presents a geared elevator machine which has several relatively small electric motors driving a single traction sheave. In this way a machine is achieved that needs only a relatively small floor area. The machine presented in GB 2116512 A can be accommodated in a machine room space not larger than the cross-sectional area of the elevator shaft below it. Such an advantageous machine room solution has not been usable in the case of the large gearless elevators because these typically have a machine with one large motor that extends a long way sideways from the traction sheave. The specification of EP 565 893 A2 presents a gearless elevator machine comprising more than one modular motor unit, which are connected together to drive traction sheaves also connected together. In such a solution, the length of the machine increases as its capacity is increased by adding a motor module. The problem in this case is that the length of the machine is increased on one side of the traction sheave, which is why the machine extends beyond the width of the elevator shaft below. Supporting and stiffening such a long machine so that its own weight and the rope suspension will not produce harmful deformations is likely to result in expensive and difficult solutions. For instance, the bending of a long machine requires a special and expensive bearing solution. If bending or other forms of load produce even the slightest flattening of the traction sheave to an elliptical shape, this will probably lead to vibrations that reduce the traveling comfort provided by the elevator.
It is an object of the present invention to achieve a new gearless elevator drive machine which develops a torque, power and rotational speed preferably as needed in large and fast elevators.
With the solution of the invention, the present torque is developed by means of two motors or motor blocks, the torque being thus doubled as compared with a single motor. The axial forces generated by the two motor blocks compensate each other, thus minimizing the strain on the bearings and motor shaft.
With the drive machine of the invention, due to the present good torque characteristics of the machine, a large traction sheave size in relation to the size, performance and weight of the drive machine is achieved. For instance, an axle load of 40000 kg can be handled by a machine weighing below 5000 kg, even if the elevator speed is as high as 9 m/s or considerably higher.
As the structure of the drive machine allows large rotor and stator diameters in relation to the traction sheave diameter, a sufficient torque on the traction sheave is easily generated. On the other hand, a short distance between the bearings in the direction of the axis of rotation automatically ensures small radial deflections, so that no heavy structures are needed to prevent such deflections.
Especially in the case of elevator drive machines with the highest requirements regarding load capacity, having a single traction sheave driven by at least two motors helps obviate the relatively high costs in relation to load capacity of large individual motors. By placing the traction sheave between two motors, a compact machine structure is achieved, as well as a possibility to transmit the torque, power and forces directly from the machine to the traction sheave without a separate drive shaft. By coupling the rotors of two different electric motors mechanically together with the tractions sheave, these advantages are achieved to a distinct degree.
The very close integration of the rotor parts of the motor with the traction sheave results in a machine in which the rotation parts practically function as a single block, allowing improved accuracy in the control of elevator movements.
As the frame of the drive machine is used both as a shell of the motor/motors and as a carrier of the bearings of the moving parts, the total weight of and the space required by the machine are relatively low as compared with conventional hoisting machines designed for corresponding use.
In principle, bearings are only needed for each rotor, whose bearing boxes are easy to seal. Any lubricant that may pass through the sealing can easily be so guided off that it will cause no harm.
Because the traction sheave is attached substantially to the junction between the rotor blocks or because the traction sheave joins the rotor blocks together along a circle of a fairly large radius, the torque developed by the motor is transmitted directly from the rotor to the traction sheave.
In the drive machine of the invention, the air gaps can be adjusted in pairs so that they will be of equal size, and the mutual air gap sizes of the two motors/motor blocks can even be adjusted so that the motors/motor blocks will look the same to the electric drive. In this way it is possible to have two motors/motor blocks driven by a single electric drive without incurring differences in the behavior of the motors/motor blocks due to the drive machine being driven by a single electric drive.
Due to its small size and light weight with regard to its load capacity, the machine is easy to implement as in terms of both machine room layout and installation. Elevator machines with a high load capacity are often used in elevator groups comprising several elevators. As the hoisting machine can be accommodated in a machine room floor area the size of the cross-section of the elevator shaft below it, this provides a great advantage in respect of utilization of building space.